The acting head of the ATF voluntarily appeared before two congressional oversight committees and revealed that senior Justice Department officials tried to limit his communications with Congress about an investigation into a controversial ATF program known as "Fast and Furious," according to a letter from the heads of two oversight committees.

The House Oversight and Government Reform Committee and U.S. Sen. Charles Grassley, R-Iowa, have been investigating the program where ATF agents recorded and tracked straw purchases of weapons and allowed the guns to "walk" across the U.S. border into Mexico in an effort to locate major weapons traffickers.

Rather than appear with lawyers from the Justice Department and the ATF, Acting Director Ken Melson hired his own private attorney and secretly appeared before congressional investigators on July 4th. According to sources close to the investigation, Melson had previously wanted to testify before the oversight committees but Justice Department officials sought to delay his testimony.

Melson's testimony came for the Congressional committee came weeks after three current ATF agents who were involved with the program testified before Congress about the botched operation and how ATF failed to stop guns from going to Mexico.

The operation took a tragic toll in December 2010 when two weapons found on the scene where Border Patrol agent Brian Terry was murdered were linked to the ATF program. According to reports by the ABC affiliate in Phoenix, other guns have now also been linked to additional crimes.

ATF officials say they were trying to build cases that would allow them to target senior drug cartel leaders and key weapons traffickers not low-level gun runners.

According to a letter to Attorney General Eric Holder from Rep. Darrell Issa, R-Calif., chairman of the House Oversight and Government Reform Committee and Sen. Grassley, Melson expressed dismay over how the operation was run and that "he was sick to his stomach" when he reviewed internal documents. The letter also notes that Melson's testimony corroborated information that DEA and FBI may have had a role in the operation.

The letter sent to Attorney General Holder notes of Melson's testimony: "He was candid in admitting mistakes that his agency made and described various ways he says that he tried to remedy the problems. According to Mr. Melson, it was not until after the public controversy that he personally reviewed hundreds of documents relating to the case, including wiretap applications and Reports of Investigation (ROIs). By his account, he was sick to his stomach when he obtained those documents and learned the full story."

Melson testified that he and top management at ATF moved to reassign supervisors working on Fast and Furious and that officials at DOJ allegedly tried to prevent ATF from notifying the oversight committees about the full nature of the management moves. The letter sent to Holder notes, "If his account is accurate, then ATF leadership appears to have been effectively muzzled while the DOJ sent over false denials and buried its head in the sand. That approach distorted the truth and obstructed our investigation. The Department's inability or unwillingness to be more forthcoming served to conceal critical information that we are now learning about the involvement of other agencies, including the DEA and the FBI."

The letter further notes on that issue, "[Melson] said that ATF was kept in the dark about certain activities of other agencies, including DEA and FBI. Mr. Melson said that he learned from ATF agents in the field that information obtained by these agencies could have had a material impact on the Fast and Furious investigation as far back as late 2009 or early 2010."

"The evidence we have gathered raises the disturbing possibility that the Justice Department not only allowed criminals to smuggle weapons but that taxpayer dollars from other agencies may have financed those engaging in such activities," Issa and Grassley noted.

According to the letter based on Melson's testimony Justice Department officials in the Office of the Deputy Attorney General (ODAG) have not been forthcoming with the congressional investigation. "Mr. Melson provided documents months ago supporting his concerns to the official in the ODAG responsible for document production to the Committees, but those documents have not been provided to us."

Melson has been acting director of ATF since April 2009. Before that he oversaw the Executive Office of U.S. Attorneys and held the office after the U.S. Attorney's scandal rocked the Bush Justice Department. Prior to that Melson was a long-time career prosecutor in the Eastern District of Virginia where he served as the top career official in the U.S. Attorney's Office.

Late Wednesday the Justice Department responded to the revealing letter that Reps. Issa and Sen. Grassley sent to Attorney General Eric Holder.

In the letter signed by Assistant Attorney General Ronald Weich the Department notes that Attorney Holder has requested an independent review of the Fast and Furious operation by the Department's Inspector General and that DOJ has made witnesses available for interviews on a voluntary basis.

"While we do not question the Committee's right to conduct appropriate oversight, we reject entirely any suggestion that our extraordinary efforts have been designed to limit- rather than facilitate- the Committee's access to information," Weich wrote.

Recently there have been several news accounts that officials were trying to oust Melson from DOJ. In their letter to Attorney General Holder the lawmakers who previously have been very critical of Melson and his tenure at ATF have changed their tune and urge the Attorney General to ensure Melson is not treated unfairly, "Given his testimony, unless a permanent director is confirmed, it would be inappropriate for the Justice Department to take action against him that could have the effect of intimidating others who might want to provide additional information to the Committees."